The objective of the proposed work is to determine the mechanism by which plasmalogens are biosynthesized in the brain and heart by using cell-free systems. We have shown that in the brain plasmalogens are synthesized from 1-alkyl-2-acyl-sn-glycerophosyphorylethanolamine by a desaturase system that involves the microsomal mixed-function oxidase system. The system appears to be similar to the one responsible for the desaturation of fatty acids. During the next year we plan to carry out studies with cell-free preparations from the heart to see if plasmalogens are made there by the same mechanism as in the brain. Further studies on the details of the reaction in the brain will also be studied. We also plan to investigate the role of plasmalogens in essential fatty acid metabolism in the brain and other tissues.